Diamond tools have high hardness which has been utilized to machine materials such as Al, Al alloy, Mg, and Mg alloy for cutting, grinding, and the like. Because surfaces finished by diamond tools are remarkably aesthetic, the diamond tools have been used for cutting and grinding technologies requiring no polishing. However, diamond tools have been extremely bad at machining oxides and iron. This is because carbon has a high tendency to bond with oxygen and because carbon reacts with iron and accordingly diamond is likely to wear. A tool of diamond or the like capable of machining oxides and iron can be a very useful tool.
In order to suppress wear of diamond, Japanese Patent Laying-Open No. 3-232973 (PTD 1) discloses a diamond tool having a surface of diamond such as sintered diamond coated with a hard surface layer of Al2O3, TiN, ZrN, BN or the like. Moreover, Japanese Patent Laying-Open No. 2010-240812 (PTD 2) discloses a surface-coated cutting tool including a base material such as diamond sintered body and a coating formed on the base material. The coating is a physically vapor-deposited film and includes a nitride layer with a thickness of 7 to 15 μm formed on the base material, a composite wear-resistant layer with a thickness of 3 to 10 μm formed on the nitride layer, and an AlN layer with a thickness of 0.2 to 5 μm formed on the composite wear-resistant layer. In the composite wear-resistant layer, a carbonitride thin layer with a thickness of 0.2 to 1.5 μm and a thin nitride film with a thickness of 0.2 to 1.5 μm are alternately laid on one another. Moreover, Japanese National Patent Publication No. 2010-527802 (PTD 3) discloses a coated diamond including: a diamond base material; a first carbide layer of a carbide-forming element; a second layer of a refractory metal selected from the group consisting of W, Mo, Cr, and the like, or a combination or an alloy thereof, substantially excluding the carbide-forming element of the first carbide layer; and an overcoating of Ag, Ni, Cu, or the like, or a combination or an alloy thereof, in which the metal is different from the metal of the second layer.